Heavy rail

Heavy rail, also known as rapid transit, subway, metro and the underground, is a high-capacity rail/train-based form of public transportation implemented in urban areas where high-density exists. Subway trains can carry up to 1500 passenger in "crush conditions." In order to increase speed and cost-effectiveness (rapid transit stations are costly to build and maintain), usually heavy rail stations are further apart than those of other kinds of networks, such as light rail or bus rapid transit.